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  #31  
Old 08-03-2002, 08:41 PM
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Quote:
Originally posted by stephenson
Not likely can be waterpump.
The water pump was the problem on my 84 300TDT. Similar situation to diesel don's. Would run ~90-100something driving, but when idling, the temps would go all the way to the top of the gauge. Fluid was flushed, T-stat changed, hoses and cap checked, etc. Finally replaced the water pump and that fixed it. Took me quite a while, so not something I could've tackled away form the garage.
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  #32  
Old 08-04-2002, 12:13 AM
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Well SSharma, the upside to all that you did is that now you have yourself a new cooling system, so you shouldn't have any problems anytime soon that way!
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  #33  
Old 08-05-2002, 11:21 AM
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SSharma,

What was the failure mechanism for the waterpump? Were the impeller blades broken?

If there was a pressure leak, it is possible ... i.e. such an extreme bearing or seal issue ... however, I assumed this would be readily apparent with steam rising from the weep hole or loss of coolant through the o ring.

I can't see how a pump that has good bearings and seal with intake impeller blades can be a problem with overheating.

Were any other services or replacements conducted at the same time?
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1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #34  
Old 08-05-2002, 03:10 PM
djwhite
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Dear folks: I am working on a similar problem with 81 TD turbo...engine running at 100C around town and close to 120C when I went to Tahoe through the hot central valley a couple of weeks ago. Coming back I hit red on Donner Pass and pulled over. Did not lose much fluid and after 30 min wait made it up and over at about 115C. When home I ran all the tests that you can find on an older thread from last year (use the search function) and narrowed it to fan clutch and radiator. I replaced the fan clutch because it was not putting out and dropped normal op temp very slightly, then I pondered doing the citric acid flush described in the CD and have some on order before spending $317 for the new behr rad. I do have a hot top hose and a coolish lower hose so I was not certain about this. While I was pondering this I noticed that the oil cooler fins were clogged with the normal engine oil/dirt sludge that you find on the side of the engine (from blow by out of the oil filler cap area, etc). So I sprayed the oil cooler fins with Gunk engine degreaser and waited the 10 mins and blew out the fins from the back with a high pressure washer. This dropped my operating temp 15C ! Now I am running at 85C I am HOPING this will do it. I did a stress test on a steep hill yesterday and never went over 100C so it looks good. I guess the point is that problems with the oil cooler are separate from the radiator proper. Both get replaced with a new rad but how nice to save the $ if you can.
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  #35  
Old 08-05-2002, 04:45 PM
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djwhite,

Interesting! So, the point is that the poor performance of a clogged oil cooler makes a massive difference in the coolant temperature? Sounds plausible ...

You talked about replacing everything except the thermostat ... maybe you did, already? It's the cheapest, easiest thing to replace ... if you didn't, what was the thought process of not doing it?

I have been following the overheating threads this year ... I had just gone through something like this on my 350 SDL - it followed swapping out the viscous fan coupling and the waterpump ... started immediately getting much hotter. I replaced the tstat and immediately back to normal temps - has been 101F here in Washington, DC area for last three weeks - stays firmly below 100C no matter what the conditions. Runs at 85C at 75MPH or 30 MPH in 101F.
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1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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  #36  
Old 08-05-2002, 05:21 PM
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djwhite:

very cool news on your oil cooler. i'll be trying that deal pretty soon. i checked the condensor over well but didn't do much with the oil cooler.

thanks for the idea

don
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  #37  
Old 08-05-2002, 05:32 PM
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Quote:
Originally posted by stephenson
djwhite,
You talked about replacing everything except the thermostat ... maybe you did, already? It's the cheapest, easiest thing to replace ... if you didn't, what was the thought process of not doing it?
Wrong! The radiator cap is the cheapest and easiest!!
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  #38  
Old 08-05-2002, 06:17 PM
djwhite
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Wallnight: I did not mean to say that I replaced everything. I meant to say that I looked at the old threads on this subject and considered the analyses you will find there. My Tstat is only about one year old. My understanding is that if it is working properly the Tstat expands at the correct temp (some dispute about what that is - 85 -104C?) to close the bypass and shunt the collant all to the rad instead of back to the water pump. The CD illustrations are quite clear on this. Therefore if it is working properly you should have a hot top hose after the engine reaches operating temp. If it is not working properly the top hose will not be as hot because the hot coolant is still circulating back to the water pump and engine. If your top hose is hot and the bottom hose is cool, the rad is working. The question is how well is it working? Lots of people know about that simple test, but it overlooks the oil cooler which is the thing I stumbled upon and which I wanted to contribute here. So the answer to your question is that I knew I had a newish tstat, I knew my rad was working but not how well, I knew I did not have pressure in my system when cold so I did not have a cracked block or gasket, I knew my cap was ok because I lost so little fluid on Donner pass, I knew I had the right coolant ratio because I tested that, I did rplace the t sender (no change). I suspected a bad dash gage or an inefficient rad. I now think it was clogged fins in the oil cooler, I may still do the citric acid flush. Don't know
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  #39  
Old 08-06-2002, 04:19 PM
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I've been reading this thread with much interest as my car has been running hotter over the past year. It gets to 100C quickly and doesn't come down much unless I'm running down hill. I also notice that the temp doesn't seem to drop much when I come to a stop and let it idle. I've suspected the fan clutch, so I just checked it according to earlier posts on this thread. With the engine stopped, my fan is easy to turn by hand whether the engine is cold or over 100C. As per posts on this thread, that means my fan clutch is shot. But I also searched other posts about fan clutches and they say that is not an indication of a bad clutch. I've just priced a new clutch at $126, so it's not something I want to buy unless I'm absolutely sure. Are there other tests for this clutch? BTW, I've had my radiator boiled out a couple of years ago, new thermostat etc. Car ran cooler after having these done, but it's running hot again.
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  #40  
Old 08-06-2002, 04:55 PM
djwhite
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Dave: The fan clutch test that I am familiar with is as follows: Get the engine hot so you would expect the bimetal contact to activate the clutch. Race the engine with one hand while holding the other hand in a position that would feel the fan blast. You should feel a blast of warm air if the clutch is working properly. The second test requires an assistant. Race a hot engine and shut it off while observing the fan. If the clutch is working properly the fan should stop at once with the last rotation of the belt. If the fan keeps spinning the clutch is shot. BTW your price is probably good as it retails for $175. It is a complicated part and you have to handle it carefully to avoid damaging the bimetal strip. It is supposed to be shipped and stored on end. Very quick and easy to install however
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  #41  
Old 08-06-2002, 05:07 PM
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Thanks DJ.

Did that test this way: Got car hot, opened hood, hit kill button while car was idling and the fan turned for about 2 seconds after belt stopped turning. Sounds like it's shot?
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  #42  
Old 08-06-2002, 06:06 PM
djwhite
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Dave: It does not sound definitive from your description. It does sound like the clutch is at least inefficient. What about the other test? I did not test mine after I replaced it so I can't tell you what it should look like when new until I check. I do not know wx 2 secs at idle means it is shot. Maybe someone else on the thread can tell you. I do not blame you for wanting to avoid the cost. BTW how did they "boil" your radiator? I thought you had a plastic radiator like mine. All I can do is flush it and use the 10% citric acid treatment.
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  #43  
Old 08-06-2002, 06:41 PM
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benchracer,

The clutch is a viscous clutch, which means it is not a mechanical, no slip event. The bimetallic spring activates the cluch by allowing oil to enter a chamber with a hydraulic type of transmission that is capable of handling a fixed value of torque. the spring is activated by the temperature of the air blowing over the hub of the clutch assembly from the radiator.

At low engine speeds it is presumed the car is travelling slower and when the clutch is "on" it is close to a 1:1 input to output connection. This goes up to around 2800 rpm or so, when the fan load begins to exceed the torque capability of the hydraulic transmission, and the fan slips. The higher the engine speed the higher the slip once the speed at which the slipping starts is exceeded (on a fan like load the torque demand increases with the square of the speed so the limit is pretty well defined). When you shut it off it is expected the fan will turn a few revolutions as the rate the engine slows down will exceed the torque capability of the clutch again.

Locking the clutch has been proposed as a potential "keep it simple..." solution, but the fan may not be structurally sound enough to last at engine speeds much over the speed the clutch slips at. Consequently, if the clutch goes bad, it should be fixed and probably not locked.

A better test of the clutch is to listen to the roar when the fan is engaged and the engine is revved to 3000 or so rpm. If the noise grows to a near offensive roar with the hood open the clutch is likely ok. If it stops spinning quickly after you shut the engine off you have more confirmation the clutch is not dead.

If the fan is not making more noise as the engine speed increases, and you are at the 105 degrees C or so when the fan is supposed to be turning with the engine speed up to the clutch limit the clutch is likely shot. When you shut the engine off the fan should go on spinning for quite a few seconds, as if the clutch is shot it will not be able to stop the fan any better than it could drive it.

Hope this helps. Jim
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Owned:
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  #44  
Old 08-06-2002, 11:55 PM
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Quote:
Originally posted by djwhite
BTW how did they "boil" your radiator? I thought you had a plastic radiator like mine.
Dennis,
The top of my radiator is plastic. I was replacing the thermostat a couple of years ago, leaned against the line that goes to the overflow tank and broke the plastic nipple on top of the radiator. Removed the radiator, took it to a local radiator shop which replaced the top plastic and told me they boiled it out.

Thanks Jim. I'll give it a listen tonight on my way home from work. I don't think the fan noise is increasing with engine speed.
That and the fact that I can easily turn the fan when engine is hot but not running - it's looking more and more like the clutch.
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1995 C280
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  #45  
Old 08-07-2002, 09:41 AM
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When my 1983 300D is hot, the fan stops immediately when the engine stops turning. There is no delay at all. You can actually see the fan jerk to a stop like the engine does during the last second of movement.

Joe
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